Flexible catheters are commonly used for invasive diagnostic and therapeutic procedures in the cardiovascular system. Such catheters are inserted percutaneously into a vein or artery, and then guided by the physician to the desired location in the blood vessels or heart. Generally, curves present in the blood vessels result in the catheter being urged against the blood vessel wall as the catheter progresses.
Pathological conditions, for example local stenoses, may cause blood vessels to narrow and impede the movement of the catheter. If the physician attempts to push the catheter past such a stenosis, the force may cause a dissection of the wall of the blood vessel or break loose a large piece of plaque, which can then lodge in a downstream vessel and impede blood flow there. For this reason, cardiovascular catheterization of atherosclerotic patients and others having pathologies of the vascular system is frequently a painful and difficult procedure.
Physicians commonly use fluoroscopy or other imaging techniques to assist them in visualizing the location of the catheter inside the body and guiding the catheter to the desired location. Fluoroscopy, however, exposes the patient to undesirable radiation. Furthermore its ability to detect narrowings of the blood vessels is limited, requiring the injection of a radio-opaque contrast medium or radioactive marker substance into the bloodstream, and its usefulness is generally limited to gross navigation of the catheter.
Some catheters include means for steering their distal tips, which the physician can use to guide the catheter around curves and past obstructions such as narrowed blood vessels. However, they give the physician no advance warning to prevent the catheter from striking obstructions, such as local stenoses, in the blood vessels or to assist in maneuvering the catheter around such obstructions.
U.S. Pat. No. 5,492,131, to Galel, which is incorporated herein by reference, describes a catheter system in which a catheter is advanced through a physiological lumen in a fully automatic manner, navigating according to a pre-determined "road map" of the lumen. A position sensor adjacent to the distal end of the catheter is used to provide feedback for catheter navigation.